Battery Life
shanebaty
Posts: 30
I have a question about how long a battery would last before needing to charge again.
I have a 240mA LiPo battery. I have hooked up a multimeter in between my power supply and circuit to measure the amount of amps it is pulling and I am getting about 42mA.
Any help explanation would be great! Thanks!
I have a 240mA LiPo battery. I have hooked up a multimeter in between my power supply and circuit to measure the amount of amps it is pulling and I am getting about 42mA.
Any help explanation would be great! Thanks!
Comments
but you are using an average of 42mA =240/42 =5.7
Then it would last 5.7hours
Using an avarage of 10mA with a 100mAh battery= 10hours and so on.
Unfortunately this is the best case scenario. In real life the battery will usually last a bit less than this calculated value. Not sure what is done for small batteries but for some of the larger ones the capacity was measured at or near the optimum load current so as to provide the best rating. Any other load current usually provided a lower rating. It is however useful for comparison purposes.
A CR2032 240ma non-rechargeable coin cell lipo at 42ma might last less than 2 hours (I have such a board with a CR2032 battery clip - big mistake LOL).
A CR123A lipo battery without regulation is a fair choice for Propeller running in RCFAST mode and can last several days running a few COGs.
The figures only relate to a brand new battery at a specified temperature that has been freshly charged according to the manufacturers instructions, which is not the normal situation - reduce your expectation of the capacity somewhat to allow for this. For a rechargeable that's been used a lot expect the capacity to drop to a fraction of that of a new cell. In particular don't discharge a battery completely, this usually causes a large permanent drop in performance.
The CR2032 example someone posted is a good example of where this simple model of battery capacity breaks down - lithium button cells are rated for no more than a few mA so that the ten-hour rate is meaningless, a thousand hour rate might be more useful a measure. If you want a button cell to give more then a couple of mA use alkaline cells like the LR44.
For retail non-rechargeable batteries manufacturers seldom condescend to provide specifications or any indication of capacity on the packaging, a disgraceful situation in the industry, but there it is.
Since the charger fills the battery in the right way, the only thing left to watch is the discharge. For 3.2-3 volt batteries it may not be wise to drop below 2.8 volts; for 3.6-7 volt batteries it may not be wise to go below 3.0 volts. When you go too low, the battery short circuits and is beyond repair, it can also be dangerous to recharge. I suppose that is why Lithium batteries start with a slow charge -- to test for a safe condition.
Lithium has about 6 times the capacity as more tradition batteries, recharges faster, stores better for longer periods and over a greater range of temperature. So it looks as though all the rest will one day disappear - like a paper soda straw.
You can get them in a bit longer than a AA at 1100mah or in an 18650 format (up to 3000mah) that is closer to the traditional round cell as I have yet to build a nice adapter for a cell phone flat pack. Parallax even has a charger/holder board.
Good advice. I've done this often.
3 AA NiCad batteries at 1.2V each are a good match too. Wish there was a cheap off-the shelf 3 AA hand-held enclosure.
Battery life certainly depends on how things are connected and used.
One of the things "I've read on the internet" is that some chemistries can discharge down to nothing without damage as long as it's a single cell. The problem of too much discharge is caused by unequal charge states amoung the cells which can cause a sort of reverse charge on a cell.
I think it's the NiCd and LiMH cells that can take take complete discharge if it's a single cell. (At least that's what some internet site said so it must be true.)
I'm pretty sure LiPos (and lead acid) will be damaged by too much discharge even if they are the only cell.
I generally use a rule that the useful capacity of a good cell is 80% of what it is rated at. So 80% * 240 mAh = 192 mAh. 192 mAh / 42mA = 4.57 hours endurance.
The further a LiPo is discharged, the fewer cycles it will last. I would derate the endurance to promote battery health and call it four hours max.
This configuration with BOE disabled lasted 9 days.
I accidentally left the TX power on overnight and it killed one of the cells in the pack. Since then, I use one of these alarms to keep me from draining another pack too low.
voltalarm-18987.jpg
Another really useful item to use with LiPos is this battery meter.
I know the battery meters are also available from eBay.
Erco told me about these battery meters (and gave me one, thanks erco).
Both of these devices plug into the balancing port of a LiPo pack.
-Phil
-Phil
My brain inserted "polymer" where you had the word "primary". Yep, no need to baby a disposable cell.